Downey Jr hits Scarlett Johansson

Hollywood actor Robert Downey Jr has reportedly knocked his Avengers co-star Scarlett Johansson while fiddling with the high-tech gadgets in his Iron Man costume.

Downey, 46, was wearing his heavy superhero suit while he was waiting to film scenes with his glamorous co-star in their new movie The Avengers, Contactmusic reported.

However, he suddenly hit the 'wrong' button which controls one of the arms and hit Johansson - who plays Black Widow in the movie - in the face.

"Robert triggered a switch that controls one of his arms -and it suddenly jerked backward and whacked poor Scarlett. Knocked silly, she staggered backward, then lost her balance and fell off the low platform they were standing on," a source said.

Stunned crew members rushed to help Johansson.

"Robert, who couldn't help because he literally can't move in that iron suit, was beside himself - he kept apologizing and saying, Oh, my God, I'm so sorry!' But Scarlett was a good sport and smiled about the incident," the sorce added.